This invention relates to radioactive seed patches, and more particularly to its use as an implant for prophylactic cancer therapy.
Interstitial radiation therapy for use in tumor and cancer therapy has a long history. Metal needles, i.e. seeds, encapsulating radioactive isotopes have long been used to treat tumors. Since 1965 the use of Iodine-125 seeds has provided a low-energy brachytherapy source, the use of which results in reduced radiation exposure to medical personnel, patients and their families. With seeds of Iodine-125 encapsulated in a material such as titanium, shielding is provided by the surrounding tissue and the seeds can be left in the patient permanently.
A number of techniques have been developed for handling the radioactive seeds. In one technique, hollow metal needles are inserted into the tumor and the seeds are thereafter inserted into the needles while the needles are being retracted to deposit the seeds in the tumor. However, the use of needles has disadvantages and problems. Since the implant is performed through an open surgical wound, the needles can only be placed straight in a straight line or at an angle dictated by the relationship of the incision to the tumor.
Another disadvantage of the above technique is that the seeds are deposited in a track made by the needle. When the needle is withdrawn, there is a tendency for the seeds to migrate in that track resulting in a poor distribution of the seeds. Poor distribution of seeds can result in undesirable concentrations of seeds resulting in either an overdosage or underdosage of radiation.
Another disadvantage to the above technique is that the seeds are small, i.e. in the order of 4.5 mm in length and 0.8 mm in diameter. The seed is small because it must fit in small bore needles which minimally change or damage tissue. The seed has a high seed surface dose and is difficult to handle because of its small size and can be easily lost and difficult to label. In addition, the technique of implantation of individual seeds is time consuming.
In another technique, plastic catheters or threads are sutured on or in the area to be treated and seeds placed therein by insertion of a nylon tube carrying the seeds. After the desired treatment period, the nylon tubes are removed. The problem with this technique is that the catheters are difficult to place so as to provide the proper dose distribution. It is also difficult to accurately space the catheters in parallel array over irregular surfaces and to anchor the catheters to the tissue. Irregular spacing can result in radiation overdose or underdose. Also, where the ends of the catheters are brought to the surface of the skin and sutured in place, there is an incipient source of contamination.
U.S. Pat. No. 4,754,745 to B. S. Horowitz discloses another technique. Horowitz discloses a conformable sheet of material which is absorbable in living tissue and has a plurality of radioactive seeds in a predetermined array within the sheet. The fundamental problem with the Horowitz technique is that the seed holder is absorbable. Horowitz's sheet material is absorbable in a period of from about 70 to 120 days. However, the iodine-125 needles used with the sheet are radioactive for approximately one year. When the sheet is absorbed into the tissue, there is nothing but tissue to hold the radioactive needles in place. This will permit some seed migration within the tissue and can result in undesirable concentrations of seeds resulting in either an overdosage or underdosage of radiation.